1. Field of the Invention
The present invention relates to an apparatus for fabricating a semiconductor device and a method for using the same. More particularly, the present invention relates to an apparatus and method for low pressure chemical vapor deposition utilizing multiple chambers and vacuum pumps.
2. Description of the Related Art
In a general low pressure chemical vapor deposition (LPCVD) apparatus, a plurality of reaction chambers rather than a single chamber are used by connecting the reaction chambers to a common wafer transfer chamber. When a process such as a thin film forming process is conducted in each of the multiple reaction chambers, a source gas is introduced into each chamber. When the process is finished, the remaining source gas within the reaction chamber must be completely evacuated before the next process can begin.
The serial supply and evacuation of source gas cannot be performed without utilizing pumping equipment connected to the plurality of reaction chambers. For a typical process, the internal pressure of the reaction chamber must be maintained close to a given target pressure during a period from before the introduction of a source gas to a predetermined time after the supply of that gas has stopped. The given target pressure condition is necessary to ensure efficient formation of the thin film within desired tolerances.
In general, the pressure within the reaction chamber varies before, during, and after the introduction of the source gas. That is, in an initial time interval before the gas is introduced, the inside of the reaction chamber must be maintained at a constant high vacuum state, for example at pressures of 10.sup.-4 Torr or below, to completely remove impurities from the other gases formerly introduced into the reaction chamber. When the gas is introduced the target pressure can be significantly higher than the initial pressure, for example, the target pressure for a thin film deposition process can be 10.sup.-3 or greater. After the deposition process, the supply of source gas is cut off, and the pressures must be returned to the high-vacuum state of the initial time interval to remove the source gas and other impurities.
A high-vacuum pump is required to keep the internal pressure of the reaction chamber at the very low pressures during the initial state, e.g., less than 10.sup.-4 Torr. Thus, a high-vacuum pump is connected to each reaction chamber. Also, a low-vacuum pump is connected to each reaction chamber to assist the high-vacuum pump.
The low-vacuum pump is used when a large load is applied to the high-vacuum pump, that is, when the source gas flows into the reaction chamber. When the source gas flows into the reaction chamber faster than the high-vacuum pump can remove it, the internal pressure of the reaction chamber increases with time. In addition, to reach the target pressure the internal pressure of the reaction chamber must be increased above the design pressure of most high-vacuum pumps. Thus, to maintain the inside of the reaction chamber at a target pressure, and to return the internal pressure of the reaction chamber to the initial state after the process, a low-vacuum pump is needed to assist the high-vacuum pump.
However, when a source gas is not being supplied to the reaction chamber, and after the pressure in the reaction chamber has decreased sufficiently to be within the design range of the high-vacuum pump, the high-vacuum pump is used alone to simply maintain the reaction chamber at a constant initial pressure.
A conventional LPCVD apparatus for manufacturing a semiconductor device includes a plurality of reaction chambers and pumping equipment connected to the reaction chambers. The conventional LPCVD apparatus and the method of using it are described with reference to the attached drawings.
FIG. 1 shows a plurality of reaction chambers and pumping equipment connected thereto which comprises a conventional LPCVD apparatus for manufacturing a semiconductor device. FIG. 2 shows the timing charts for fabricating a semiconductor device using the LPCVD apparatus having the configuration shown in FIG. 1.
Referring to FIG. 1, a conventional LPCVD apparatus for manufacturing a semiconductor device comprises a plurality of pumping components connected to a plurality of reaction chambers. A first load lock chamber 16 and a second load lock chamber 18 allow a wafer to be placed into the apparatus before starting a process. First, second, and third reaction chambers 10, 12 and 14, respectively, are used for performing various semiconductor fabricating processes. A transfer chamber 8 transfers wafers from the load lock chambers 16 and 18 to the reaction chambers 10, 12 and 14, and back, and is positioned between the load lock chambers 16 and 18 and the reaction chambers 10, 12 and 14.
A pair of high-vacuum pumps 10a and 10b are connected in parallel to the first reaction chamber 10. A low-vacuum pump 10e is connected in series to the pair of high-vacuum pumps 10a and 10b through a pair of gate valves 10c and 10d, respectively. The two high-vacuum pumps 10a and 10b connected to the first reaction chamber 10 are referred to as the first and second high-vacuum pumps, respectively.
The second reaction chamber 12 is similarly connected to two parallel high-vacuum pumps 12a and 12b and in series through two gate valves 12c and 12d, respectively, to a low-vacuum pump 12e. Finally, the third reaction chamber 14 is similarly connected to two parallel high-vacuum pumps 14a and 14b and in series through two gate valves 14c and 14d, respectively, to a low-vacuum pump 14e. The two high-vacuum pumps 12a and 12b connected to the second reaction chamber 12 are referred to as the third and fourth high-vacuum pumps, respectively. Also, the two high-vacuum pumps 14a and 14b connected to the third reaction chamber 14 are referred to as the fifth and sixth high-vacuum pumps, respectively. The three low-vacuum pumps 10e, 12e and 14e, respectively connected to the first, second, and third reaction chambers 10, 12 and 14, are referred to as the first, second and third low-vacuum pumps, respectively.
The two gate valves 10c and 10d between the first and second high-vacuum pumps 10a and 10b, and the first low-vacuum pump 10e, are referred to as the first and second gate valves, respectively. The two gate valves 12c and 12d between the third and fourth high-vacuum pumps 12a and 12b, and the second low-vacuum pump 12e are referred to as the third and fourth gate valves, respectively. Finally, the two gate valves 14c and 14d between the fifth and sixth high-vacuum pumps 14a and 14b, and the third low-vacuum pump 14e are referred to as the fifth and sixth gate valves, respectively.
In the conventional LPCVD apparatus, the pumping equipment consists of a pumping component connected to each reaction chamber. The pumping component consists of two high-vacuum pumps, two gate valves, and one low-vacuum pump. A process using the conventional LPCVD technology is described with reference to FIG. 2.
FIG. 2 shows the operation of the first through sixth gate valves (10c, 10d, 12c, 12d, 14c and 14d in FIG. 1), the operation of the first through sixth high-vacuum pumps (10a, 10b, 12a, 12b, 14a and 14b in FIG. 1), and the first through third low-vacuum pumps (10e, 12e and 14e in FIG. 1) as determined by whether the reaction gas is supplied or not to the first through third reaction chambers 10, 12, and 14. In detail, reference numerals 20, 22 and 24 are timing charts for illustrating the pressure state of the first through third reaction chambers 10, 12, and 14 over a given period of time. Reference numerals 26, 27, and 28 are timing charts for opening and closing the three pairs of gate valves associated with the first through third reaction chambers, respectively.
Referring to the timing chart 20 of the first reaction chamber 10, the wafer loaded therein is heated for a period of time called a first time section 20a ("Temp Inc") to a predetermined temperature, such as an appropriate depositing temperature for forming a thin film. After the first time section 20a, a reaction gas is introduced into the first reaction chamber 10 for a period of time referred to as a second time section 20b ("Gas Flow"). In the second time section 20b, the internal pressure of the first reaction chamber 10 increases as illustrated by time chart 20. For example, in a thin film deposition process the internal pressure 20 is about 10.sup.-7 Torr during time section 20a. However, the internal pressure 20 increases to about 10.sup.-3 Torr in the second time section 20b. Thus, the first and second high-vacuum pumps 10a and 10b are operated together with the first low-vacuum pump 10e during the second time section 20b.
The reaction gas is cut off at the end of time section 20b and does not flow during a third time section 20c ("Anneal"). The gas that remains from time section 20b is evacuated at the beginning of time section 20c until the first reaction chamber internal pressure 20 returns to its initial value. Time section 20c continues for a predetermined duration depending on the specific process. For example, during time section 20c, an annealing step in a thin film formation process is conducted for stabilizing the thin film, and the remaining gas within the first reaction chamber 10 is removed to clean the inside of the first reaction chamber in order to prevent impurities from being additionally deposited on the wafer. In the third time section 20c, after the pressure 20 of the first reaction chamber returns to the initial state, the first and second high-vacuum pumps 10a and 10b can be operated alone. During time sections 20a through 20c, the first and second gate valves associated with the first reaction chamber 10 connected thereto are always open as illustrated by time chart 26.
While the first reaction chamber 10 operates in the first and second time sections 20a and 20b as shown in the time chart 20, the second reaction chamber 12 operates in a fourth time section 22a as shown in time chart 22. For example, the second chamber 12 may be performing an annealing process and stabilizing the wafer by heating the same. Later, while the first reaction chamber 10 is in the third time section 20c, the second reaction chamber 12 goes through a fifth time section 22b when a gas is introduced and the chamber pressure increases to a low-vacuum state, and through a sixth time section 22c when the gas is removed and the chamber returns to a high-vacuum state. For example, in a thin film formation process a reaction gas is supplied during time section 22b and an annealing process occurs during time section 22c.
Simultaneously, the third reaction chamber 14 begins in a seventh time section 24a at the high-vacuum state as shown in time chart 24. For example, time section 24a can be utilized for annealing the wafer and stabilizing it by heating it to a predetermined temperature. While both the first reaction chamber 10 and the second reaction chamber 12 are in the high vacuum state during times sections 20c and 22c, respectively, the third reaction chamber 14 has a gas that is introduced during an eighth time section 24b. Then the gas is evacuated during a ninth time section 24c. For example, a thin film can be formed on the wafer during the eighth time section 24b, and a subsequent annealing process can occur in the ninth time section 24c.
In the second and third reaction chambers time charts 22 and 24, the second and third low-vacuum pumps 12e and 14e, respectively, should be operated during the fifth and eighth time sections 22b and 24b, respectively, for maintaining the internal pressure during gas flow at the low-vacuum state. They also should be operated during the sixth and ninth time section 22c and 24c, respectively, to return the reaction chambers to the initial high-vacuum state. The third and fourth gate valves associated with the second reaction chamber remain open as illustrated by time chart 27. Similarly, the fifth and sixth gate valves associated with the third reaction chamber remain open as illustrated by time chart 28.
As described above and illustrated by time charts 26, 27 and 28, the first through sixth gate valves are always open regardless of the supply of reaction gas to the first through third reaction chambers illustrated by time charts 20, 22, and 24.
Note that the first through sixth high-vacuum pumps 10a, 10b, 12a, 12b, 14a and 14b and the first through third low-vacuum pumps 10e, 12e, and 14e can also always be on. Also, as shown in FIG. 1, note that each reaction chamber is connected in series to a pair of parallel high-vacuum pumps and one low-vacuum pump. Two gate valves are disposed between the pair of high-vacuum pumps and the single low-vacuum pump. The low-vacuum pump can be used when each reaction chamber is at an initial vacuum state as well as when the reaction gas is supplied to the reaction chamber; but, the low-vacuum pumps are unnecessary except for when the reaction gas is supplied to the reaction chamber.
In any case, a LPCVD apparatus for fabricating a semiconductor device by the conventional technology requires many vacuum pumping components, which require a large amount of management, maintenance, expense, and floor space diverted from valuable semiconductor fabrication facilities.